Psychology of Personality Exam 3 Study Guide Chapter 6 Objectives Understand the hierarchy of the genome e g Chromosomes are made up of what Genes are made up of what Genome Chromosomes Genes DNA Know the difference between a phenotype and a genotype Genotype an organism s genetic information Phenotype an organism s observable characteristics Know the goals of behavioral genetics Behavioral genetics to what degree are individual differences due to genetic environmental factors Determine What of trait differences is due to genetics what is due to environment Behavioral geneticists typically are not content simply with figuring out the percentage of variance due to genetic and environmental causes Percentage of variance refers to the fact that individuals vary or are different from each other and this variability can be partitioned into percentages that are due to different causes How do genes and environment interact What environmental effects are important e g parents teachers peers Be able to define and describe heritability and enviromentality Heritability how much an individual difference is explained by genetics Refers to the proportion of observed variance in a group of individuals that can be accounted for by genetic variance It describes the degree to which genetic differences among individuals cause differences in an observed property such as height extraversion or sensation seeking Environmentality how much of an individual difference is due to environment Be able to recognize examples of common misconceptions about heritability Heritability CANNOT be applied to single people A single individual s height for example is not 90 due to his her genes It is more accurate to say that the variation between people in height is 90 due to genetic differences Is NOT constant unchangeable Ex Heritability can be high in one population e g among Swedes but low in another e g among Nigerians Is NOT a precise statistic Error or unreliability of measurement for example can distort heritability statistics And because heritability statistics are typically computed using correlations which themselves fluctuate from sample to sample further imprecision creeps in Heritability is best regarded merely as an estimate of the percentage of phenotypic differences due to genetic differences Be able to list define and describe the four methods used in behavioral genetics What are some ways that you could measure the extent to which personality differences in the population are due to genetics Selective Breeding obviously not with humans Family Studies Twin Studies Adoption Studies See below for descripitons Know how each of the four methods used in behavioral genetics can provide information about the heritability of traits e g How can studying twins help scientists to determine the heritability of extraversion Selective breeding Can t be done ethically with humans Ex Selective breeding of dogs The fact that heritability has been so successful with dogs tells us that heredity must be a factor in the personality traits such as aggressiveness agreeableness and desire to please that were successfully selected Family Studies Correlates genetic similarity w personality similarity If trait is very heritable more genetic relatedness more similarity on traits Ex If dad and son are both high sensation seekers 2nd cousin is not could be genetics Problem Families typically share genes environment Family studies are never definitive Twin Studies Monozygotic vs Dizygotic twins Monozygotic twins Share a single fertilized egg a single zygote monozygotic Share 100 of their genes Dizygotic twins Come from two separately fertilized eggs two zygotes dizygotic Monozygotic vs Dizygotic twins Estimate heritability Are identical monozygotic MZ twins share 100 of genes more similar than fraternal dizygotic DZ twins If MZ twins are more similar than DZ twins due to heritability Equal environments assumption What is a problem with this assumption The twin method assumes that the environments experienced by identical twins are no more similar to each other than are the environments experienced by fraternal twins If they are more similar then the greater similarity of the identical twins could be due to the fact that they experience more similar environments rather than the fact that they have more genes in common If identical twins are treated by their parents as more similar then fraternal twins are treated by their parents For example if the parents of identical twins dress them in more similar clothing than do the parents of fraternal twins then the greater similarity of the identical twins might be due to more similar treatment Adoption Studies Positive correlations on traits between adopted children adoptive parents environmental influence Positive correlations between adopted children genetic parents genetic influence Adoption studies get around equal environments assumption Representativeness Are adopted children adoptive genetic parents representative of the general population Adoption studies assume that adopted children their birth parents and their adoptive parents are representative of the general population Ex these studies assume that couples who adopt children are not any different from couples who do not adopt children Several studies have confirmed that the assumption of representativeness holds for cognitive abilities personality education level and even socioeconomic status Selective Placement Does a child s adoptive parents tend to be similar to his or her genetic parents If adopted children are placed with adoptive parents who are similar to their birth parents then this may inflate the correlations between the adopted children and their adoptive parents Fortunately there does not seem to be selective placement so this potential problem is not a problem in actual studies Know the difference between monozygotic and dizygotic twins Know the major findings of behavioral genetics that were discussed in class See above The Big Five Extraversion 40 60 heritable Neuroticism 30 54 heritable Sexual orientation Controversial developing area Genes modest indirect influence on adult sexual orientation 20 67 heritability A lot of variance in heritability Some show high heritability ex traditionalism 34 63 Others show low no heritability ex belief in god Researchers don t agree on exactly what makes an attitude heritable or not Activity level showed a heritability of 4 suggesting that a moderate proportion of the
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